FIG. 1 shows a conventional door push bar structure that is mounted on a door 5 by extending a mounting bolt 4 through a predetermined position on the door 5, so that an expanded head portion 41 of the mounting bolt 4 is pressed against an outer side of the door 5; and connecting two push bars 51, 52 to two opposite ends of the mounting bolt 4. The push bar 51 that is connected to the expanded head portion 41 of the mounting bolt 4 is provided with a stop element 53, so that the push bars 51, 52 are attached to the door 5 at desired positions. A user may then apply a force on the push bar 51 or 52 to open or close the door 5.
However, since the push bars 51, 52 are installed on the door 5 simply by screwing the mounting bolt 4 through the door 5 into an end of the other push bar 52, frequent pull or push of the push bars 51, 52 would cause loosening of the push bars 51, 52, particularly the push bar 52, from the door 5 to result in unstable connection of the push bars 51, 52 to the door 5. Moreover, there doors 5 with different thickness. For a thicker door 5, a longer mounting bolt 4 is needed to secure firm connection of the push bar 52 to the door 5. Reversely, for a thinner door 5, a shorter mounting bolt 4 is sufficient for use. Therefore, many differently sized mounting bolts 4 have to be prepared for mounting the push bars 51, 52 on doors 5 with different thickness. This would inevitably result in increased material cost for the mounting bolts 4 as well as inconveniences and confusions to the workers mounting the push bars.